When coating components, it is often desirable or necessary to carry out only a partial coating of components and, in subsequent steps, optionally to provide the areas to be left clear in the respective coating process with other coating materials or to leave these areas to be left clear completely uncoated. Thus it is desirable for example to keep areas which are imprinted or are to be imprinted, for example with a barcode, free of coating. It may also be necessary to leave uncoated areas around passage openings for example for measuring probes or areas around blind holes to which screw connections are to be attached. The areas to be left clear can also be provided for attaching electrical contacts or for other purposes.
Methods by which partial coatings can be carried out are known from the state of the art. Thus DE-A-43 34 131 describes a method in which ferromagnetic objects are partially coated by first providing the areas to be left clear with a permanent-magnetic film and then coating the ferromagnetic objects. Because of the magnetic forces, the films are attracted to the surface of the ferromagnetic object, closely covering it. The film can be removed after the coating and the area to be left clear remains untreated. However, a disadvantage is that the method can be used only with ferromagnetic materials. Furthermore, it takes time to remove the film again after the coating.
A method for coating elements with a plurality of openings is known from DE-A-29 40 582, in which shaped parts are inserted into the openings of the element to be coated, wherein the coating agent is applied to the element in a thickness which is less than the projecting height of the shaped parts. The shaped parts have a conical, pyramidal or gable roof-like shape, wherein in each case the inclination angle of the shaped surface abutting the associated opening of the element is larger than that of the element surface bordering the openings. The shaped surface abuts the top edge of the opening, sealing it in a linear manner. A disadvantage with this method is that a covering of further surrounding areas around the opening is not possible. Furthermore, a sufficiently secure arrangement of the shaped parts in the openings is not guaranteed.
It is known from U.S. Pat. No. 5,328,723 to use plug-like covering means which have a conical section, with a round cross-section, which can be inserted into the recess and consist of a thermoplastic foam. A sufficiently reliable covering of the areas to be left clear is not guaranteed by means of this covering, in particular in the case of automated coating processes. Furthermore, the two last-mentioned methods of the state of the art have the disadvantage that the partial coating of smooth surfaces not provided with recesses or holes is very time-consuming or not possible.
A method which makes possible the partial coating of smooth surfaces which are not provided with recesses or holes is disclosed in DE-A-10 149 892. In this method, metal surfaces to be treated are partially protected by first covering the area of the metal surface, which is to be left clear and not treated, with a fluid acting as protective layer. This is transformed from a liquid aggregate state into a solid aggregate state by exposure to light and/or radiation or by heat extraction. The surface treatment then takes place and the protective layer is then removed again. This method has been developed for the partial electroplating of surfaces.
Catalytically active layers cannot be partially applied to shaped bodies with this method. The protective layer which cures through heat extraction, thus is liquid at higher temperatures, mixes in the liquid state with the applied washcoat suspension. Furthermore, the protective layer cannot be removed by dissolving it with a solvent if it is covered with a washcoat layer. Shaped bodies cannot be partially provided with a washcoat coating using this method.
DE 101 49 892 A1 describes a method for partially applying a coating to a metal surface by means of a surface treatment, in particular an electroplating treatment, in order to obtain areas with a coating and areas without a coating. The parts of the metal surface not to be coated are first covered with a fluid acting as protective layer which is transformed from a liquid aggregate state into a solid aggregate state by exposure to light and/or radiation or heat extraction, a surface treatment follows and then the protective layer is removed again.
DE 10 2004 058 705 B3 discloses a disposable masking method for a thermal coating method as well as a corresponding thermal coating method, wherein the disposable masking is constructed from moistened particles compressed together in a female mould.
EP 1 510 592 A1 also describes a partial method for coating a component, wherein a masking is applied which consists at least in part of a ceramic powder and can be removed after the coating of the component. This document does not disclose thermal removal.